Telecommunications services generally fall into two major categories: broadcast services, in which all user terminals receive the same information, and switched services, in which each user terminal receives information specific to him/her. Network infrastructures can be similarly classified. An example of a broadband infrastructure is a conventional CATV network, while an example of a switched infrastructure is the public switched telephone network (PSTN). In general, it is more cost effective to deliver broadcast services on broadcast networks and switched services on switched networks.
While the thrust of the present invention is broadcast telecommunication services, and thus, typically one-way service, broadcast telecommunication services can also include two-way services for interactive services e.g., shopping and games and may include audio as well as video. Two-way services may include information, interactive shopping and games and other services. The upstream portion of the telecommunications would be provided in a known manner and not necessarily in the manner described for the present invention. Upstream services could, however, be combined with the downstream broadcast services of the present invention described herein.
Recent work has shown that the optical properties of certain passive devices can be exploited to permit a given infrastructure to emulate properties of both switched and broadcast infrastructures and thus efficiently provide both switched and broadcast service. In particular, the cyclical properties of Waveguide Grating Routers (WGRS) used in conjunction with Wavelength Division Multiplexing (WDM) provide flexible partitioning of both types of networks using the same physical infrastructure. WGRs are also sometimes called Arrayed Waveguide Grating (AWG), Phased Array (Phasar) or Dragone Routers. The WGR acts as the distribution element at the remote node. Any reference, therefore, to a WGR should be deemed to encompass any such device or other known device for performing similar functionality.
Much work has been done recently to demonstrate the possibilities of such a system to deliver large quantities of digital TV carriers. A particularly robust QPSK (quadrature-phase-shift-keying) transmission format permits the use of low quality and potentially inexpensive optical sources with wide optical bandwidths. In particular, it has been shown that the wavelength domain can be used to deliver “blocks” of television programming channels (one RF block per wavelength band) in a similar manner to known analog block converters. These demonstrations have been shown to deliver multiple 500 MHz blocks of QPSK modulated carriers of, for example, television channels from a Satellite service provider, using the location of the optical band as a multiplexing index.